VENUS TRANSIT INFORMATION

WHAT'S HAPPENING

Astronomical Transit - "the passage of a smaller celestial body or its shadow across the disk of a larger celestial body."

The Planet Venus will Transit across the face of the Sun. The event can be witnessed by using the appropriate Sun Filter on Binoculars or Telescope, or the technique of Solar Projection.

If you have good sight, then normal Eclipse Glasses will surfice.

*NEVER LOOK AT THE SUN WITHOUT THE APPROPRIATE SOLAR FILTER*.

Diagram of Locations Where the Transit Can be Seen

The disk (face) of Venus will have around 58 arc seconds of angular diameter (how big it is).
1 degree = 60 minutes, 1 minute = 60 seconds. This is the around the largest Venus gets at its closest point to us. Using trigonometry, knowing the diameter
of the planet allows us to calculate its distance, and vica versa.

WHERE'S IT HAPPENING

Venus follows the same path as the Sun and Moon across the sky. Since Venus's orbit is closer to the Sun than ours (inferior planet), the planet can be generally seen at dawn, dusk or twilight and is the brightest object in the sky except for the Moon. Venus itself, cannot be seen during the day since the Sun is too bright. The Transit time
will depend on your location. Please see Diagram above and information below:

WHERE CAN I SEE IT FROM?

Part or all of the Transit can be seen from just about any location on the Earth. Unfortunately, some places will not be in a position to see it. These include New Zealand, Fiji, Tonga, Hawaii and Western parts of the Americas.

WHEN'S IT HAPPENING

The Transit will last more than 6 hours from start to finish. On the 8th of June at 05:08 UT (Universal Time) the Transit will begin. Local times are below:

The Transit will be best seen through a pair of Binoculars or Telescope using the appropriate Solar Film, Wielding Glass No. 12 or stronger, or via Solar Projection. The Transit can be seen using Eclipse Glasses under good conditions (high in the sky) with good eyesight. The disk of Venus will be 1/32th the diameter of the Sun. As the Sun gets lower in the atmosphere, it will be harder to observe unaided.

SAFETY

Looking at the Sun even for a few seconds can cause irreversible damage.

Using filters in the eyepiece are dangerous because the heat is concentrated on the eyepiece. One crack....
possible blindness.

USING TELESCOPES FOR THE VENUS TRANSITPlease Note:

*The Appropriate Solar Filter still needs to be used for this technique.*

*Ensure Any Caps Made are securely attached to the Telescope and cannot be blown or knocked off*

*Always Cover the Finderscope to prevent accidental blindness* - To align the Telescope with the Sun, look at the Telescope's Tube shadow on the ground and adjust so the shadow is perfectly round (outside of tube).

Solar Filter caps which fit over the end of your telescope are available.
Let us know your telescope diameter.

Solar projection onto a piece of cardboard or similar is a good way to view the Transit and Sun Spots. If your
using a large reflecting telescope, only use a
small hole to gather the light. A cheap eyepiece like Huygen
(Hoi-gen) or Ramsden is best. They do not use glue to hold the lenses together inside the eyepiece
(it
will melt!). We have them available.

Remember to place a filter over the finderscope of your telescope or block it off all together to prevent
eye damage from the curious wondering what your
looking at. Also, the finderscope can cause a burn and
in some plastic cases - melt!

STOPPING DOWN A TELESCOPEPlease Note:

*The Appropriate Solar Filter still needs to be used for this technique.*

*Ensure Any Caps Made are securely attached to the Telescope and cannot be blown or knocked off*

*Always Cover the Finderscope to prevent accidental blindness* - To align the Telescope with the Sun, look at the Telescope's Tube shadow on the ground and adjust so the shadow is perfectly round (outside of tube).

Increased clarity, along with a longer focal ratio, decreased brightness and the ability to use
the best part of your mirror is some of the advantages of Stopping Down a Telescope.

Disadvantages are a reduced Field of View.

Cut out a cardboard or similar disk about the same diameter as your tube. This will be
placed over the end of the telescope (where the light goes in). From the disk, cut holes
in the places where only the mirror sees (no obstruction). eg. between secondary mirror arms,
around the secondary mirror, or even if your focuser sticks in too far creating an obstruction.
Keep the cornering of the circles neat. Oblongs are ok. Each hole is now your mirror without
the obstruction of the secondary mirror, arms and maybe focuser which steal resolution.
Your new size mirror changes the focal ratio of the telescope to a longer one making it great
for Moon, planets and Transits - as long as the subject is bright enough for you now, smaller
mirror. Using circles in the disk makes it easier to work out your new focal ratio etc.
Circles also allow you to choose what part of the mirror is used by rotating the disk.

MORE TRANSIT STUFF

INTERESTING EFFECT

As the black disk of Venus fully enters the Sun's Disk, a black trail appears to stay connected to the edge of the disk of the Sun. This lasts for a small period of time. The unexpected effect is liken to a drop of water clinging to a surface as it drops. This is also known as "teardrop". Another way of recreating the affect is to put your fingers together in front of your eyes. As the gap decreases, the edges of your fingers become blurred. Turbulence, the differences between light and dark and Venus' atmosphere, are amoungst the reasons thought to be causing this effect.

THE RARE TRANSIT

On June 8th Venus will pass in front of the Sun. The event is very rare having last occured in 1882. There are always 2 transits of Venus relatively close to each other. The next being in 8 years.

OBSERVABLE LOCATIONS

New Zealanders will unfortuneatly miss the event since the transition will start at sunset. As we move west, the event will start earlier in the day when the Sun is higher and easier to observe. Observers in Sydney will witness the start around 3.00pm. For observers in the middle of Australia (Adelaide), Venus will start its transition around 2.30pm. The entire event will be widely visible from the Europe, Africa and Asia. The transition will last for about 6 hours.

EVENT SIGNIFICANCE FOR MEASUREMENT

Significance of the event include a determination of the Astronomical Unit (au). The Astronomical Unit is based on the average distance between the Earth and the Sun and is mainly used to measure objects in the Solar System.

One way of measuring distances is to use Angular Measurement. One of the different ways of Angular Measurement is Triagulation Method. An observer can obtain the angle from the observed diameter of the object. Knowing the angle allows us to calculate the distance. While Venus transits the Sun, another measurement can be taken which is the diameter of the Sun. Having an extra measurement allows more accuracy as both measurements can be compared. eg. distance from Venus to Sun.

Observed diameters of objects are measured in Arc Seconds. An Arc Second is derived thus:

There will be many schools and organisations taking their own measurements. The Angular Mesurement taken by some will be by Secular Parallax. This basically uses measurements from 2 locations on the Earth to form a triangle to Venus. Since its been 181 years since the last mesaurement, we are certainly due for an update!

Data taken from the 1761 and 1769 Transits were not used until over a century later to determine the Sun's distance. This is because the technology of calculations had not yet been discovered. The measurement taken at that time is accurate to 0.1 percent.
Other, more accurate means of measuring the average distance to the Sun have been used the since the last transit. Today's figure is 1,495,978,706,974 -/+ 0.0003km (accurate to 33cm)

INTERESTING HISTORY FOR AUSTRALIANS

When Captain Cook made his original voyage south in 1769, it was to observe the transit of Venus from Tahiti. The scientific importance of the transit was to use it to measure distances in the solar system. Captain Cook was specifically chosen because he was amougst the very few who knew how to work out longitude. Together with his seamanship, he was a particularly special person, and only he could have made the voyage. During the voyage, he opened his secondary secret orders which reveiled he was to discover the great southern land (Australia) and claim it for Britain.

IR FILTERS FOR PHILIPS TO-U-CAM

$120AUD
Since common light sources deliver light that has a very broad spectral output, reaching
beyond the visible, many visual and detector-based applications call for a filter that is
designed to pass only light within the visible spectrum. For example, monochrome (black
and white) cameras are often used with IR cutoff filters to eliminate the effects of the
presence of near infrared light incident upon the detector.

IR Blocking filters are 25mm diameter. It is a true dichroic filter and it is
MgF2 coated.

2X BARLOW / CAMERA ADAPTOR / FILTER HOLDER

$70AUD
Back in stock are these marvelous 1.25" diameter adaptors. They are able to do a number of
things. Firstly, its a achromatic 2x Barlow. Secondly, its a camera adaptor, which is
threaded, and only the T Mount is needed to suit your brand of camera. Photos can then be
taken through a telescope at higher magnification without using an eyepiece. Thirdly, the
Barlow's lens can be removed by unscrewing for true focal projection photography. Fourthly,
with the Barlow's lens removed, filters can be screwed in. - Crikey!

COLOURED FILTER
*used with Solar Filter*
$30AUD

NO. 23A LIGHT RED
Moon - Enhances lunar features.
Mars - Reduces the light from the blue and green areas which darkens the maria, oases and canal
markings while lightening the orangish desert regions. Also sharpens the boundries of yellow
dust clouds.
Mercury - Improves observation at twilight when the planet is low near the horizon and in
daylight it reduces the brightness of the blue sky to enhance surface features.
Saturn - Useful for studying the bluer clouds and the polar regions.
Venus - For daylight observing it reduces the brightness of the blue sky. Occasionally
deformations of the terminator are visible.
Comets - Improves definition of comet dust trails.
Solar - When using Mylar Solar Filters, this filter will give you true colour rendition.